Anti-counterfeiting and information encryption system and method based on metasurface thermal radiation modulator

Abstract

The present invention relates to the field of information encryption, and specifically to an anti-counterfeiting and information encryption system and method based on a metasurface thermal radiation modulator, comprising a metal substrate layer, a dielectric layer, a graphene layer and a metal nano-antenna layer arranged in sequence from bottom to top; the metal nano-antenna layer is composed of a metal nano-antenna array; at least two pixel structures are obtained according to the size and / or arrangement period of the nano-antenna in the metal nano-antenna array, so that they have different or the same average infrared emissivity under the same excitation conditions; different pixel units composed of different pixel structures are spatially arranged in the pixel space according to various types of image information; and the information carried by the pixel space arrangement is displayed through a thermal image under set conditions by means of electrical excitation and / or infrared band selection. That is, the scheme of the present invention can realize the hiding, encryption or switching of information, and can significantly improve the flexibility and security of anti-counterfeiting and information encryption.

Description

Technical Field

[0001] The present invention relates to the field of information encryption, and in particular to an anti-counterfeiting and information encryption system and method based on a metasurface thermal radiation modulator. Background Art

[0002] Informatization is a major trend in the development of today's era. With the continuous development of information technology, the problem of information security encryption has become increasingly prominent. The traditional information encryption method mainly encodes information digitally and uses digital signal processing technology to protect the information. With the continuous increase in the amount of information, the traditional method of protecting information cannot meet the diversity of encryption methods, and various modern encryption technologies have emerged. The current mainstream encryption methods can be divided into electrical encryption and optical encryption. Compared with electrical encryption, optical encryption has the advantages of multi-dimensionality, large capacity, high design freedom, and high complexity.

[0003] In recent years, with the rise of metasurface research, the design concept of metasurfaces has been combined with optical holographic display, and multi-channel multiplexed optical metasurface encryption has been realized. Metasurfaces have powerful wavefront control capabilities and can accurately control electromagnetic field amplitude, phase, polarization and other characteristics. Optical metasurfaces provide a new platform for optical information encryption, hiding, encoding and other technologies.

[0004] Although optical information encryption technology continues to advance and has been widely used, it still faces some challenges, such as the need to further improve security and encrypted information capacity. In addition, as our lives and sensitive information become more and more digital, the demand for new encryption technologies is becoming more and more urgent. Existing optical information encryption methods are already well known, and how to innovate some new information encryption methods is also an important issue that needs to be solved in this field.

[0005] Infrared rays are electromagnetic waves with wavelengths between microwaves and visible light; in nature, all objects can radiate infrared rays. Under the condition that only the absorption of atmospheric molecules is considered, the atmosphere has four atmospheric infrared "transmission windows" in near infrared (0.78μm~1.0μm), short-wave infrared (1.0μm~2.5μm), medium-wave infrared (3μm~5μm) and long-wave infrared (8μm~13.5μm). Using infrared thermal imaging technology, the infrared radiation energy distribution of the target can be detected and received, and the infrared radiation intensity signal of the object can be converted into a pseudo-color image and graph that can be distinguished by human vision. This infrared thermal image corresponds to the thermal distribution field on the surface of the object. Therefore, the invisible infrared energy emitted by the object can be converted into a visible thermal image using an infrared thermal imaging system. This image information loaded in the infrared band has a natural encryption advantage because it cannot be directly obtained by the human eye. According to the Stefan-Boltzmann law, the radiation capacity of an object is determined by its emissivity and temperature. By covering it with a specific material or structure, the infrared radiation characteristics of the target can be changed, presenting a false temperature field distribution under an infrared camera. For example, covering the surface of a target with a low-emissivity material can suppress the infrared radiation characteristics of the target, merge the thermal infrared radiation characteristics of the target with those of the background, reduce the probability of it being discovered by infrared detection equipment, and achieve thermal camouflage.

[0006] In view of the powerful electromagnetic wave control capability of metasurfaces, the thermal radiation modulator based on tunable metasurface design can generate different infrared radiation intensities. By using infrared equipment to obtain the spatial distribution of infrared radiation spectrum intensity of metasurface structures, the hidden patterns, numbers or characters on the metasurface can be transformed into visible thermal images under certain conditions. The anti-counterfeiting, information encryption and identification methods and systems combining tunable metasurfaces and infrared thermal imaging technology can expand the existing information encryption methods, have the advantages of strong concealment and high security, and have important application prospects in the fields of high-end anti-counterfeiting and information encryption.

[0007] However, the prior art does not provide specific means for regulating information encryption. Summary of the invention

[0008] In order to solve the above technical problems, the purpose of the present invention is to provide an anti-counterfeiting and information encryption system and method based on a metasurface thermal radiation modulator. The specific technical solution is as follows:

[0009] The present invention provides a technical solution for an anti-counterfeiting and information encryption system based on a metasurface thermal radiation modulator, comprising a metal substrate layer, a dielectric layer, a graphene layer and a metal nano-antenna layer arranged in sequence from bottom to top;

[0010] The metal nano-antenna layer is composed of a metal nano-antenna array, and at least two pixel structures are obtained according to the different sizes and / or arrangement periods of the metal nano-antennas in the metal nano-antenna array, and the at least two pixel structures have different or the same average infrared emissivity under the same excitation conditions;

[0011] The pixel structure is formed into a pixel unit, and the pixel units are spatially arranged in a pixel space according to various types of image information, each pixel unit includes a pixel structure, and different pixel structures form different pixel units and are represented by different colors;

[0012] By means of electrical excitation and / or infrared band selection, the information carried by the spatial arrangement of pixels can be displayed through thermal images under set conditions.

[0013] Further, according to the difference of the metal nanoantenna array, that is, the difference of the size and / or arrangement period of the metal nanoantennas constituting the array, four pixel structures are obtained, including pixel structure 1, pixel structure 2, pixel structure 3 and pixel structure 4;

[0014] The four pixel structures are arranged in an array on a plane according to the pattern or character information they carry. Under different excitation conditions, the thermal image presents different images.

[0015] Furthermore, the excitation condition is that the average infrared emissivity of different pixel structures under the same infrared band and different electrical excitations is:

[0016] Under the first electrical excitation, the pixel structure 1 and the pixel structure 2 have the same first average infrared emissivity, the pixel structure 3 and the pixel structure 4 have the same second average infrared emissivity, and the absolute value of the difference between the first average infrared emissivity and the second average infrared emissivity is greater than a set value;

[0017] Under the second electrical excitation, pixel structure one and pixel structure three have the same third average infrared emissivity, pixel structure two and pixel structure four have the same fourth average infrared emissivity, and the absolute value of the difference between the third average infrared emissivity and the fourth average infrared emissivity is greater than the set value.

[0018] Furthermore, under the excitation condition of the same electrical excitation and different infrared bands, the average emissivity of different pixel structures is:

[0019] In the first infrared band, the pixel structure 1 and the pixel structure 2 have the same first average infrared emissivity, the pixel structure 3 and the pixel structure 4 have the same second average infrared emissivity, and the absolute value of the difference between the first average infrared emissivity and the second average infrared emissivity is greater than a set value;

[0020] In the second infrared band, pixel structure one and pixel structure three have the same third average infrared emissivity, pixel structure two and pixel structure four have the same fourth average infrared emissivity, and the absolute value of the difference between the third average infrared emissivity and the fourth average infrared emissivity is greater than a set value.

[0021] Furthermore, four pixel structures are realized by setting the codes to "00", "01", "10" and "11".

[0022] Furthermore, based on the differences in the metal nanoantenna arrays, i.e., the sizes and / or arrangement periods of the metal nanoantennas constituting the arrays, two pixel structures are obtained, including a first pixel structure and a second pixel structure; the two pixel structures are arranged in an array on a plane according to the pattern or character information they carry, and the thermal image does not display information when no electrical excitation is applied, and when electrical excitation is applied, the information carried by the spatial arrangement of the pixels is obtained.

[0023] Furthermore, the two pixel structures have the same average infrared emissivity when no electrical excitation is applied; they have different average emissivities when electrical excitation is applied, and the difference between the average emissivity when no electrical excitation is applied and the average emissivity when electrical excitation is applied is greater than or equal to a set value; the two pixel structures are realized by setting the codes to "0" and "1".

[0024] Furthermore, the metal nanoantenna is composed of a metal micro-nano structure, the micro-nano structure is in the shape of a disc or a square patch, the thickness of the metal nanoantenna layer is 0.1-0.2 μm; the thickness of the dielectric layer is 0.5-2 μm; the graphene layer is a few-layer graphene film, and the number of graphene layers is 2-10.

[0025] Furthermore, the electrical excitation is to use the graphene layer and the metal substrate layer on the metasurface thermal radiation modulator as electrodes, connect an external circuit, and apply different voltages or electrical excitations to modulate the Fermi energy or conductivity of the graphene layer to regulate its thermal radiation performance, wherein the external voltage tuning range is -5V to 5V.

[0026] The present invention also provides an encryption method using the above-mentioned anti-counterfeiting and information encryption system based on the metasurface thermal radiation modulator, comprising the following steps:

[0027] When different excitation conditions are applied to the metasurface thermal radiation modulator, the thermal images show different images:

[0028] When the anti-counterfeiting and information encryption system based on metasurface thermal radiation modulator has two pixel structures,

[0029] When in the same infrared band, the two pixel structures are arranged in an array on a plane according to the pattern or character information they carry. When no electrical excitation is applied, the infrared thermal image does not display information, and when electrical excitation is applied, the information carried by the pixel spatial arrangement is obtained;

[0030] When the anti-counterfeiting and information encryption system based on metasurface thermal radiation modulator has four pixel structures,

[0031] When in the same infrared band, the four pixel structures are arranged in an array on a plane according to the pattern or character information they carry. Under the first electrical excitation, an infrared thermal imager is used to collect a thermal image, and the thermal image presents a first image; under the second electrical excitation, the thermal image presents a second image;

[0032] When the same electrical excitation is applied, the four pixel structures are arranged in an array on a plane according to the pattern or character information they carry. In the first infrared band, the thermal image presents a first image, and in the second infrared band, the thermal image presents a second image.

[0033] Beneficial effects of the present invention:

[0034] The present invention adopts an electrically controlled graphene metasurface thermal radiation modulator to construct an infrared anti-counterfeiting and information encryption system. By selecting a graphene metasurface thermal radiation modulator structure that meets certain thermal radiation performance requirements (infrared average emissivity) as different pixel units of the infrared anti-counterfeiting and information encryption system, combined with voltage control and / or infrared wavelength selection control means, the information carried by the pixel space arrangement is presented through an infrared device, and the information is hidden, encrypted or switched, which can significantly improve the flexibility and security of anti-counterfeiting and information encryption. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 It is a structural schematic diagram of the anti-counterfeiting and information encryption system based on the metasurface thermal radiation modulator of the present invention;

[0037] Figure 2 A schematic diagram of a pixel unit including a pixel structure of the anti-counterfeiting and information encryption system based on a metasurface thermal radiation modulator of the present invention;

[0038] Figure 3A schematic diagram of a pixel unit including four pixel structures of the anti-counterfeiting and information encryption system based on a metasurface thermal radiation modulator of the present invention;

[0039] Figure 4 A graph showing the relationship between the actual surface temperature of the metasurface thermal radiation modulator of the present invention and the radiation temperature indicated by the infrared thermal imager;

[0040] Figure 5a Emission spectra of the metasurface thermal radiation modulator corresponding to the pixel structure coded as “0” in the two preferred pixel structures of Example 1 of the present invention when the graphene Fermi energy is 0 eV and 0.3 eV respectively;

[0041] Figure 5b Emission spectra of the metasurface thermal radiation modulator corresponding to the pixel structure coded as “1” in the two preferred pixel structures of Example 1 of the present invention when the graphene Fermi energy is 0 eV and 0.3 eV respectively;

[0042] Figure 6 Schematic diagram of the spatial arrangement of two types of pixel units in the anti-counterfeiting and information encryption system of Example 1 of the present invention;

[0043] Figure 7a An infrared thermal image or temperature field distribution diagram of the anti-counterfeiting and information encryption system based on the metasurface thermal radiation modulator of Example 1 of the present invention when the graphene Fermi energy is 0 eV;

[0044] Figure 7b An infrared thermal image or temperature field distribution diagram of the anti-counterfeiting and information encryption system based on the metasurface thermal radiation modulator of Example 1 of the present invention when the graphene Fermi energy is 0.3 eV;

[0045] Figure 8a The emission spectra of the metasurface thermal radiation modulator corresponding to the pixel structure coded as "00" among the four pixel structures preferred in Example 2 of the present invention at graphene Fermi energies are 0.3 eV and 0.9 eV respectively;

[0046] Figure 8b The emission spectra of the metasurface thermal radiation modulator corresponding to the pixel structure coded as "01" among the four pixel structures preferred in Example 2 of the present invention at graphene Fermi energies are 0.3 eV and 0.9 eV respectively;

[0047] Figure 8c The emission spectra of the metasurface thermal radiation modulator corresponding to the pixel structure coded as "10" among the four pixel structures preferred in Example 2 of the present invention at graphene Fermi energies are 0.3 eV and 0.9 eV respectively;

[0048] Figure 8dThe emission spectra of the metasurface thermal radiation modulator corresponding to the pixel structure coded as "11" among the four pixel structures preferred in Example 2 of the present invention at graphene Fermi energies are 0.3 eV and 0.9 eV respectively;

[0049] Fig. 9 Schematic diagram of the spatial arrangement of four pixel units in the anti-counterfeiting and information encryption system of Example 2 of the present invention;

[0050] Fig.10a An infrared thermal image or temperature field distribution diagram of the anti-counterfeiting and information encryption system based on the metasurface thermal radiation modulator of Example 2 of the present invention when the graphene Fermi energy is 0.3 eV;

[0051] Fig.10b An infrared thermal image or temperature field distribution diagram of the anti-counterfeiting and information encryption system based on a metasurface thermal radiation modulator according to Embodiment 2 of the present invention when the graphene Fermi energy is 0.9 eV;

[0052] Fig.11 Schematic diagram of the spatial arrangement of four pixel units in the anti-counterfeiting and information encryption system of Example 3 of the present invention;

[0053] Fig.12a A thermal image or temperature field distribution diagram of an infrared window of 3-5 μm when the graphene Fermi energy is 0.9 eV for the anti-counterfeiting and information encryption system based on a metasurface thermal radiation modulator according to Example 3 of the present invention;

[0054] Figure 12b A thermal image or temperature field distribution diagram of an infrared window of 8-14 μm when the graphene Fermi energy is 0.9 eV for the anti-counterfeiting and information encryption system based on a metasurface thermal radiation modulator of Example 3 of the present invention;

[0055] The reference numerals are: 1-metal substrate layer; 2-dielectric layer; 3-graphene layer; 4-metal nanoantenna layer; 5-external circuit; a-diameter of the metal nanoantenna; p-period of the metal nanoantenna array. DETAILED DESCRIPTION

[0056] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of the scheme according to the present invention, its specific implementation, structure, features and effects in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures, or characteristics in one or more embodiments may be combined in any suitable form.

[0057] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0058] Embodiment of anti-counterfeiting and information encryption system based on metasurface thermal radiation modulator

[0059] The scheme of the present invention uses an electrically controlled graphene metasurface thermal radiation modulator to construct an infrared anti-counterfeiting and information encryption system. By preferably using a graphene metasurface thermal radiation modulator that meets certain thermal radiation performance requirements (infrared average emissivity) as the pixel structure for constructing the infrared anti-counterfeiting and information encryption system, combined with voltage control and / or wavelength selection control means, the information carried by the pixel space arrangement is presented through an infrared device to achieve information hiding, encryption or switching, which can significantly improve the flexibility and security of anti-counterfeiting and information encryption.

[0060] like Figure 1 As shown, the infrared anti-counterfeiting and information encryption system of the present invention includes a metal substrate layer 1, a dielectric layer 2, a graphene layer 3, a metal nano-antenna layer 4, and an external circuit 5 connecting the metal substrate layer 1 and the graphene layer 3, which are arranged in sequence from bottom to top.

[0061] Among them, the best number of graphene layers is 3-5 layers. This is because the tuning of thermal radiation performance by a single layer of graphene is not obvious, while when the graphene layer is too thick, the electric shielding effect is significant, which is not conducive to the tuning of thermal radiation performance.

[0062] The infrared anti-counterfeiting and information encryption system based on the graphene metasurface thermal radiation modulator includes M×N pixel units or micro-areas (M, N = 2, 3, 4...); according to the size and / or arrangement period of the metal nanoantenna in the metal nanoantenna layer of the graphene metasurface thermal radiation modulator, the M×N pixel units include 2 n A pixel structure or type.

[0063] like Figure 2 As shown, it is a structural schematic diagram of one pixel unit of the metasurface thermal radiation modulator anti-counterfeiting and information encryption system, and one pixel unit is composed of a pixel structure; the metal nanoantenna layer therein is a quadrilateral or hexagonal array of a certain number of disc-shaped metal nanoantennas, a represents the diameter of the metal disk in the metal nanoantenna layer, and p represents the period of the arrangement of the metal nanoantennas.

[0064] It should be noted that the number of metal nanoantennas contained in the metal nanoantenna layer of a pixel unit depends on the area of ​​the pixel unit and the period (p) of the metal nanoantenna array; and the spatial resolution of the infrared thermal imager determines the minimum pixel area of ​​the infrared anti-counterfeiting and information encryption system.

[0065] In order to distinguish and facilitate description, different pixel structures are coded and represented in this embodiment:

[0066] When n=1, there are two kinds of pixels, which are coded as "0" and "1"; when n=2, there are four kinds of pixels, which are coded as "00", "01", "10" and "11". Figure 3 As shown, and so on.

[0067] It should be noted that pixels with the same code have the same thermal radiation performance due to the same structure; pixels with different codes have different thermal radiation performance due to different structures, and the average infrared emissivity is different but can also be the same. When the average infrared emissivity is different, different colors are presented in the infrared thermal image. At the same time, the Fermi energy of the graphene layer can be adjusted as a whole by applying an external voltage, and the infrared radiation intensity of different pixel structures can be adjusted, showing different radiation temperatures under the infrared thermal imager and displayed in different colors; considering the temperature resolution of the infrared thermal imager, the difference in the average infrared emissivity of different pixels cannot be too small.

[0068] In this embodiment, different metasurface thermal radiation modulator structures can be obtained according to the different sizes and / or arrangement periods of metal nanoantennas, and their infrared emission spectra can be calculated to establish a corresponding database; according to the infrared emissivity requirements of the anti-counterfeiting and information encryption system for different pixel structures, the corresponding structure is selected from the database as the pixel structure for constructing the anti-counterfeiting and information encryption system, which is used to realize different forms of anti-counterfeiting and information encryption.

[0069] In this embodiment, pixel units are formed by pixel structures, and different types of pixel units containing different pixel structures are spatially arranged in the pixel space according to various types of image information; the information carried by the pixel spatial arrangement is displayed through a thermal image under set conditions by means of electrical excitation and / or infrared band selection.

[0070] It should be noted that the pixel unit in this embodiment is the most basic unit constituting an image, which may be equivalent to a pixel point; and the pixel space is the space in which the pixel units are arranged.

[0071] Specifically: the metasurface thermal radiation modulator in this embodiment is divided into two pixel structures or four pixel structures according to the size and / or arrangement period of the nanoantennas in the metal nanoantenna layer:

[0072] (1) The anti-counterfeiting and infrared information encryption system includes two pixel structures. The preferred pixel structure should meet the following infrared thermal radiation performance in the same infrared window:

[0073] The two pixel structures have the same average emissivity when no electrical excitation is applied, that is, ε1=ε2; they have different average emissivities when electrical excitation is applied, that is, ε1≠ε2, and the difference in average emissivity is not less than 0.03, that is, |ε2-ε1|≥0.03.

[0074] The two pixel units containing two pixel structures are arranged on the pixel space plane according to the pattern or character information they carry. When no electrical excitation is applied, the infrared thermal image has a uniform temperature field distribution and does not display information. When electrical excitation is applied, there is a temperature difference in different pixel areas, and the thermal image shows the information carried by the pixel space arrangement.

[0075] (2) The infrared anti-counterfeiting and information encryption system includes four pixel structures. The preferred pixel structure should meet the following infrared thermal radiation performance in the same infrared window:

[0076] Under the first electrical excitation condition, pixel structure one and pixel structure two have the same average infrared emissivity ε1, pixel structure three and pixel structure four have the same average infrared emissivity ε2, ε2≠ε1 and |ε2-ε1|≥0.03; under the second electrical excitation condition, pixel structure one and pixel structure three have the same average infrared emissivity ε3, pixel structure two and pixel structure four have the same average infrared emissivity ε4, ε4≠ε3 and |ε4-ε3|≥0.03.

[0077] Four pixel units containing four pixel structures respectively are arranged on the pixel space plane according to the pattern or character information they carry. Under the first electrical excitation condition, the infrared radiation temperature of pixel structure one and pixel structure two is different from the infrared radiation temperature of pixel structure three and pixel structure four, and the thermal image presents image one. Under the second electrical excitation condition, the infrared radiation temperature of pixel structure one and pixel structure three is different from the infrared radiation temperature of pixel structure two and pixel structure four, and the thermal image presents image two.

[0078] (3) The infrared anti-counterfeiting and information encryption system includes four pixel structures. The preferred pixel structure meets the following infrared thermal radiation performance under the same electrical excitation conditions:

[0079] In one infrared window, pixel structure 1 and pixel structure 2 have the same average infrared emissivity ε1, pixel structure 3 and pixel structure 4 have the same average infrared emissivity ε2, ε2≠ε1 and |ε2-ε1|≥0.03. In another infrared window, pixel structure 1 and pixel structure 3 have the same average infrared emissivity ε3, pixel structure 2 and pixel structure 4 have the same average infrared emissivity ε4, ε4≠ε3 and |ε4-ε3|≥0.03.

[0080] The four pixel units respectively containing four pixel structures are arranged on the pixel space plane according to the patterns or character information they carry. In the first infrared window, the infrared radiation temperature of pixel structure one and pixel structure two is different from the infrared radiation temperature of pixel structure three and pixel structure four, and the thermal image presents image one. In the second infrared window, the infrared radiation temperature of pixel structure one and pixel structure three is different from the infrared radiation temperature of pixel structure two and pixel structure four, and the thermal image presents image two.

[0081] It should be noted that the serial numbers in the above-mentioned pixel structure 1, pixel structure 2, pixel structure 3 and pixel structure 4 merely represent a serial number and there is no specific order. It depends on the presentation of the specific image, that is, the corresponding arrangement is performed according to the image information.

[0082] It should be noted that the above-mentioned metasurface thermal radiation modulator of this embodiment uses the finite element electromagnetic field simulation software Comsol Multiphysics to perform structural design, optimization and simulation calculation of its infrared radiation performance, and then obtain the pixel structure for constructing the anti-counterfeiting and information encryption system.

[0083] Specifically, in the simulation process, the metal substrate layer is replaced by a perfect conductor boundary, and the graphene layer is replaced by a surface current layer in the computational simulation, with a current density of The conductivity of graphene is total Calculation of σ using the Drude model and the interband model total =N(σ D +σ int ), N represents the number of graphene layers, σ D is the conductivity obtained by the Drude model, σ int is the conductivity obtained by the inter-band model;

[0084]

[0085]

[0086] In the formula, E F represents the Fermi energy, ω is the frequency of incident light, q is the charge of the electron, T is the temperature, k is the Boltzmann constant, h is the reduced Planck constant, τ represents the graphene carrier scattering time, and i is the imaginary unit.

[0087] For a graphene layer, by applying an external voltage, the Fermi energy E of graphene F It will increase, resulting in an increase in the electrical conductivity of graphene, showing metallic properties, high reflection and low emissivity.

[0088] By using simulation, the emission spectra of metasurface thermal radiation modulators with different metal nanoantenna arrays are calculated, and the average emissivity in the two infrared windows of 3-5μm and 8-14μm is obtained. Among them, the average infrared emissivity of the metasurface thermal radiation modulator is different, and the temperature indicated by the infrared thermal imager, that is, the radiation temperature, is also different; the radiation temperature (T a ) can be obtained by the following formula:

[0089] ε a T a 4 =ε s T s 4 +(1-ε s )T b 4

[0090] where ε a is the emissivity set by the infrared thermal imager, usually taken as 1, ε s is the average infrared emissivity of the metasurface thermal radiation modulator in the pixel area, T s and T b represent the actual surface temperature of the metasurface thermal radiation modulator in the pixel area and the ambient temperature, T s The size of can be controlled by placing the metasurface thermal radiation modulator on a heating stage.

[0091] It should be noted that the setting value in the above formula is 0.03, which is the minimum average emissivity difference that different pixel structures need to have, obtained by inverting the thermal sensitivity (minimum temperature difference) of the infrared thermal imager; Figure 4 The figure shows the relationship between the actual surface temperature of the thermal radiation modulator and the radiation temperature indicated by the thermal imager. The ambient temperature T b =27℃, the infrared emissivity of the thermal radiation modulator is between 0 and 1; Figure 4 It can be seen that when T b and T s When all are determined, the emissivity of the metasurface thermal radiation modulator is different, and the radiation temperature T indicated by the infrared thermal imager is a Therefore, the corresponding minimum emissivity difference can be determined based on the minimum radiation temperature difference that the infrared thermal imager can distinguish. Assuming T b =27℃, T s =62℃, the thermal sensitivity of the infrared thermal imager is 1℃, when the radiation temperature range is between 40℃ and 50℃, the minimum emissivity difference required for different pixel structures is about 0.03.

[0092] Based on the structure of the metasurface thermal radiation modulator described above, the following is a detailed introduction to the anti-counterfeiting and infrared information encryption system realized by the graphene metasurface thermal radiation modulator through specific application examples:

[0093] Example 1

[0094] The dielectric layer thickness of the graphene metasurface thermal radiation modulator in this embodiment is 1.15 μm, and the number of graphene layers is 5.

[0095] By optimizing the disk diameter size and / or arrangement period of the metal nanoantenna of the graphene metasurface thermal radiation modulator, two pixel structures are obtained. In order to distinguish, the codes of the two pixel structures are set to "0" and "1". The diameter of the metal nanoantenna of the pixel coded as 0 is a = 0.2μm, and the arrangement period is p = 1μm; the diameter of the metal nanoantenna of the pixel coded as "1" is a = 1.7μm, and the arrangement period is p = 2μm.

[0096] Figure 5a and Figure 5b The emissivity spectra of the two pixel structures encoding "0" and "1" in the 8-14μm infrared band when the graphene Fermi energy is 0eV and 0.3eV respectively. It can be calculated from the emissivity spectra that when there is no electrical excitation, that is, the graphene Fermi energy is 0eV, the average emissivity of the "0" pixel structure and the "1" pixel structure in the 8-14μm band is equal, that is, ε1=ε2=0.25; when an external voltage is applied to make the graphene layer Fermi energy reach 0.3eV, the average emissivity of the "0" pixel structure and the "1" pixel structure in the 8-14μm band is different, ε1=0.27 and ε2=0.6 respectively. Table 1 gives the structural parameters of the two pixels and their average infrared emissivity under different electrical excitations.

[0097] Table 1

[0098] coding 0 1 Structural parameters a=0.2μm,p=1μm a=1.7μm,p=2μm <![CDATA[Average emissivity ε(E F = 0 eV)]]> 0.25 0.25 <![CDATA[Average emissivity ε(E F = 0.3eV)]]> 0.27 0.6

[0099] The anti-counterfeiting and infrared information encryption system based on the graphene metasurface thermal radiation modulator of this embodiment includes 18×18 pixel units, which are respectively composed of the two pixel structures encoding "0" and "1". Figure 6 The pixels shown in the figure are arranged regularly in space. The black area represents pixels coded as "0" and the white area represents pixels coded as "1". When there is no electrical excitation, since the average emissivity of the two pixel structures is the same, the spatial temperature field is evenly distributed and the thermal image shows no pattern, as shown in Figure 2. Figure 7a As shown in Figure 2, when an external voltage is applied to make the graphene Fermi energy reach 0.3 eV, due to the different infrared radiation properties of the "0" and "1" pixels, at T b =27℃, T s=62℃, the calculated infrared radiation temperatures are approximately 38℃ and 49℃ respectively. Due to the large temperature difference, different pixel areas can be clearly distinguished in the thermal image, such as Figure 7b As shown, information consistent with the pixel spatial arrangement is displayed. Therefore, the anti-counterfeiting and infrared information encryption system can only display the information carried by the pixel spatial arrangement through the infrared imaging device under electrical excitation, and can be used for infrared anti-counterfeiting and information encryption.

[0100] Example 2

[0101] The dielectric layer thickness and the number of graphene layers of the graphene metasurface thermal radiation modulator in this embodiment are the same as those in Embodiment 1.

[0102] In this embodiment, by optimizing the size and arrangement period of the metal nanoantenna of the graphene metasurface thermal radiation modulator, four pixel structures are obtained, which are encoded as "00", "01", "10" and "11", which are the first pixel structure, the second pixel structure, the third pixel structure and the fourth pixel structure respectively. The structural parameters of the four pixel structures (the diameter and arrangement period of the metal nanoantenna) and their corresponding average emissivity are shown in Table 2.

[0103] Table 2

[0104]

[0105] Figure 8a-8d These are the emission spectra of four pixel structures “00”, “01”, “10” and “11” at Fermi energies of 0.3eV and 0.9eV respectively. Figure 8a-8d The results show that the average emissivity of the four pixel structures in the 8-14μm band can be calculated when the graphene Fermi energy is 0.3eV and 0.9eV respectively. When the graphene Fermi energy is 0.3eV, the average emissivity of the "00" pixel and the "01" pixel in the 8-14μm band is ε1=0.38; the average emissivity of the "10" pixel structure and the "11" pixel structure is ε2=0.52. When the graphene Fermi energy is 0.9eV, the average emissivity of the "00" and "10" pixel structures is ε3=0.44; and the average emissivity of the "01" and "11" pixel structures is ε4=0.63, as shown in Table 2 above.

[0106] The anti-counterfeiting and infrared information encryption system based on the graphene metasurface thermal radiation modulator of this embodiment includes 28×28 pixel units, and the pixel units respectively including the above four pixel structures are arranged according to Fig. 9 The pixels are arranged according to the spatial arrangement rule shown in the figure. Different pixel units are represented by different colors. The Fermi energy of the graphene layer is uniformly regulated by applying an external voltage. When the Fermi energy reaches 0.3 eV, at T b =27℃, Ts =62℃, the infrared radiation temperature of the pixel unit corresponding to the pixel structure of "00" and "01" is about 42℃, and the infrared radiation temperature of the pixel unit corresponding to the pixel structure of "10" and "11" is about 47℃. Different temperatures correspond to different colors. At this time, the thermal image presents a "static" deer pattern, such as Fig.10a As mentioned above, when the Fermi energy rises to 0.9eV, the infrared radiation temperature of the pixel unit corresponding to the "00" and "10" pixel structures is about 44°C, and the infrared radiation temperature of the pixel unit corresponding to the "01" and "11" pixel structures is about 50°C. The thermal image shows a "running" deer, as shown in Figure 1. Fig.10b shown.

[0107] Therefore, in addition to carrying pattern information, the above-mentioned anti-counterfeiting or information encryption method can also transmit character or digital information. For example, "ZHENG HANG" is disassembled into two images "ZHENG" and "HANG" transmitted under different voltages. The correct and complete information can only be obtained when a specific voltage is applied to the graphene layer and different voltages are applied in a certain order. If the real information is hidden in one of the patterns or a combination of two patterns, it can only be correctly decrypted under a specific external voltage and electrical excitation sequence. Therefore, the graphene metasurface thermal radiation modulator containing four pixels can realize multiple encryption of information.

[0108] Example 3

[0109] The only difference between this embodiment and embodiment 2 is that the degrees of freedom of regulating thermal radiation performance are different; that is, embodiment 2 optimizes the pixel structure according to the thermal radiation performance of the graphene metasurface under different electrical excitations, and transmits and switches information by regulating the external voltage; while this embodiment optimizes the pixel structure according to the thermal radiation performance of the graphene metasurface thermal radiation modulator in different infrared windows, and transmits different information by selecting the working band.

[0110] Specifically, in this embodiment, the applied voltage regulates the graphene Fermi energy to 0.9 eV, optimizes the geometric structure parameters and arrangement period of the metal nanoantenna, and preferably obtains four pixel structures, and their corresponding metal disk diameters and arrangement periods, as well as the average emissivity values ​​in the two bands of 3-5 μm and 8-14 μm are shown in Table 3. In the 3-5 μm band, the "00" pixel structure and the "01" pixel structure have the same average emissivity ε1=0.34, and the "10" pixel structure and the "11" pixel structure have the same average emissivity ε2=0.42. In the 8-14 μm band, the "00" pixel structure and the "10" pixel structure have the same average emissivity ε3=0.55; the "01" pixel structure and the "11" pixel structure have the same average emissivity ε4=0.65.

[0111] Table 3

[0112]

[0113] The four pixels are divided into Fig.11 The pixel space arrangement rule shown is arranged, and different pixel units are represented by different colors. The pixel space contains 26×26 pixel units. When applying an external voltage to make the graphene Fermi energy reach 0.9eV, when observed with an infrared device with a working wavelength of 3-5μm, the infrared radiation temperature of the pixel units corresponding to the "00" and "01" pixel structures is about 40℃, and the infrared radiation temperature of the pixel units corresponding to the "10" and "11" pixel structures is about 43℃. The thermal image shows the information of "ZHENG ZHOU", as shown in Fig.12a As shown; when observed with an infrared device with a wavelength of 8-14μm, the infrared radiation temperature of the pixel units corresponding to the "00" and "10" pixel structures is about 48°C, and the infrared radiation temperature of the pixel units corresponding to the "01" and "11" pixel structures is about 51°C. The thermal image shows the information of "HANG YUAN", as shown Figure 12b As shown. This anti-counterfeiting or information encryption method can not only carry character information, but also transmit pattern or digital information. If the real information is hidden in one of the thermal images or the combination of two thermal images, it can only be correctly decrypted under a specific external voltage (graphene Fermi energy), a specific working band, and the correct band selection order. Therefore, this system not only realizes multiple encryption of infrared thermal information, but also has higher security and concealment.

[0114] A novel infrared anti-counterfeiting and information encryption system provided by the present invention is based on a tunable graphene metasurface thermal radiation modulator; by optimizing pixel structures with different infrared radiation properties, using electrical excitation and / or infrared band selection and control means, under specific conditions, the information carried by the pixel spatial arrangement is visualized through a thermal image, thereby achieving information reproduction or decoding, which has important application value in the field of infrared anti-counterfeiting and information encryption.

[0115] Embodiment of anti-counterfeiting and information encryption method based on metasurface thermal radiation modulator

[0116] The present invention also provides an encryption method using the above-mentioned anti-counterfeiting and information encryption system based on the metasurface thermal radiation modulator, comprising the following steps:

[0117] When different excitation conditions are applied to the metasurface thermal radiation modulator, the thermal images show different images:

[0118] When the anti-counterfeiting and information encryption system based on metasurface thermal radiation modulator has two pixel structures,

[0119] When in the same infrared band, the two pixel structures are arranged in an array on a plane according to the pattern or character information they carry. When no electrical excitation is applied, the infrared thermal image does not display information, and when electrical excitation is applied, the information carried by the pixel spatial arrangement is obtained;

[0120] When the anti-counterfeiting and information encryption system based on metasurface thermal radiation modulator has four pixel structures,

[0121] When in the same infrared band, the four pixel structures are arranged in an array on a plane according to the pattern or character information they carry. Under the first electrical excitation, an infrared thermal imager is used to collect a thermal image, and the thermal image presents a first image; under the second electrical excitation, the thermal image presents a second image;

[0122] When the same electrical excitation is applied, the four pixel structures are arranged in an array on a plane according to the pattern or character information they carry. In the first infrared band, the thermal image presents a first image, and in the second infrared band, the thermal image presents a second image.

[0123] Since the anti-counterfeiting and information encryption method based on metasurface thermal radiation modulator of this embodiment is implemented based on the anti-counterfeiting and information encryption system embodiment of metasurface thermal radiation modulator, and the above-mentioned anti-counterfeiting and information encryption system embodiment based on metasurface thermal radiation modulator has been specifically introduced, it will not be repeated here.

[0124] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. An anti-counterfeiting and information encryption system based on a metasurface thermal radiation modulator, characterized in that: It includes a metal substrate layer, a dielectric layer, a graphene layer and a metal nano-antenna layer which are arranged in sequence from bottom to top; The metal nano-antenna layer is composed of a metal nano-antenna array, and at least two pixel structures are obtained according to the different sizes and / or arrangement periods of the metal nano-antennas in the metal nano-antenna array, and the at least two pixel structures have different or the same average infrared emissivity under the same excitation conditions; The pixel structure is formed into a pixel unit, and the pixel units are spatially arranged in a pixel space according to various types of image information, each pixel unit includes a pixel structure, and different pixel structures form different pixel units and are represented by different colors; By means of electrical excitation and / or infrared band selection, the information carried by the spatial arrangement of pixels is displayed through a thermal image under set conditions; According to the different sizes and / or arrangement periods of the metal nanoantennas, four pixel structures are obtained, including pixel structure 1, pixel structure 2, pixel structure 3 and pixel structure 4; The four pixel structures are arranged in an array on a plane according to the pattern or character information they carry. Under different excitation conditions, the thermal image presents different images. The excitation conditions are that the average infrared emissivity of different pixel structures under the same infrared band and different electrical excitations is: Under the first electrical excitation, the pixel structure 1 and the pixel structure 2 have the same first average infrared emissivity, the pixel structure 3 and the pixel structure 4 have the same second average infrared emissivity, and the absolute value of the difference between the first average infrared emissivity and the second average infrared emissivity is greater than a set value; Under the second electrical excitation, the pixel structure 1 and the pixel structure 3 have the same third average infrared emissivity, the pixel structure 2 and the pixel structure 4 have the same fourth average infrared emissivity, and the absolute value of the difference between the third average infrared emissivity and the fourth average infrared emissivity is greater than a set value; The excitation conditions are the same electrical excitation and different infrared bands, and the average emissivity of different pixel structures is: In the first infrared band, the pixel structure 1 and the pixel structure 2 have the same first average infrared emissivity, the pixel structure 3 and the pixel structure 4 have the same second average infrared emissivity, and the absolute value of the difference between the first average infrared emissivity and the second average infrared emissivity is greater than a set value; In the second infrared band, the pixel structure 1 and the pixel structure 3 have the same third average infrared emissivity, the pixel structure 2 and the pixel structure 4 have the same fourth average infrared emissivity, and the absolute value of the difference between the third average infrared emissivity and the fourth average infrared emissivity is greater than a set value; According to the difference of the metal nano-antenna array, that is, the size and / or arrangement period of the metal nano-antennas constituting the array, two pixel structures are obtained, including a first pixel structure and a second pixel structure; the two pixel structures are arranged in an array on a plane according to the pattern or character information carried, and the thermal image does not display information when no electrical excitation is applied, and when the electrical excitation is applied, the information carried by the pixel spatial arrangement is obtained; The two pixel structures have the same average infrared emissivity when no electrical excitation is applied; and have different average emissivity when electrical excitation is applied, and the difference between the average emissivity when no electrical excitation is applied and the average emissivity when electrical excitation is applied is greater than or equal to a set value; the two pixel structures are realized by setting the codes to "0" and "1"; When different excitation conditions are applied to the metasurface thermal radiation modulator, the thermal images show different images: When the anti-counterfeiting and information encryption system based on the metasurface thermal radiation modulator has two pixel structures, When in the same infrared band, the two pixel structures are arranged in an array on a plane according to the pattern or character information they carry. When no electrical excitation is applied, the infrared thermal image does not display information, and when electrical excitation is applied, the information carried by the pixel spatial arrangement is obtained; When the anti-counterfeiting and information encryption system based on metasurface thermal radiation modulator has four pixel structures, When in the same infrared band, the four pixel structures are arranged in an array on a plane according to the pattern or character information they carry, and under the first electrical excitation, an infrared thermal imager is used to collect a thermal image, and the thermal image presents a first image; Under the second electrical excitation, the thermal image presents a second image; When the same electrical excitation is applied, the four pixel structures are arranged in an array on a plane according to the pattern or character information they carry. In the first infrared band, the thermal image presents a first image, and in the second infrared band, the thermal image presents a second image.

2. The anti-counterfeiting and information encryption system based on metasurface thermal radiation modulator according to claim 1 is characterized in that: The four pixel structures are realized by setting the codes to "00", "01", "10" and "11".

3. The anti-counterfeiting and information encryption system based on metasurface thermal radiation modulator according to claim 1 is characterized in that: The metal nanoantenna is composed of a metal micro-nano structure, the micro-nano structure is in the shape of a disc or a square patch, the thickness of the metal nanoantenna layer is 0.1-0.2 μm; the thickness of the dielectric layer is 0.5-2 μm; the graphene layer is a few-layer graphene film, and the number of graphene layers is 2-10.

4. The anti-counterfeiting and information encryption system based on metasurface thermal radiation modulator according to claim 1 is characterized in that: The electrical excitation is to use the graphene layer and the metal substrate layer on the metasurface thermal radiation modulator as electrodes, connect an external circuit, and apply different voltages or electrical excitations to modulate the Fermi energy or conductivity of the graphene layer to regulate its thermal radiation performance, wherein the external voltage tuning range is -5V to 5V.

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